Solid experimental evidence for reverse intersystem crossing from high-lying triplet states: A case study on hot exciton mechanism in OLEDs

Authors：Chen, Liangjian; Qiao, Xianfeng^*; Xiao, Shu; Chi, Jiajin; Yang, Dezhi; Ma, Dongge^*; Ma, Yuguang

Source：Applied Physics Letters, 2022, 120(8): 083501.

DOI：10.1063/5.0081246

• LIGHT-EMITTING-DIODES
• MAGNETIC-FIELD
• EFFICIENT
• ELECTROLUMINESCENCE
• EMISSION

Hot excitons have been attempted to utilize the triplet excitons in organic light-emitting diodes (OLEDs). Due to the transient and dark nature of high-lying triplet states (T-n, n >= 2), the normative methods to characterize the hot exciton mechanism have not been thoroughly developed. Here, a normal technique combining transient photoluminescence and magneto-electroluminescence (MEL) measurements has been proven to visualize the reverse intersystem crossing process from T-2 to S-1 states in 5,6,11,12-tetraphenylnaphthacene (rubrene) molecules. Rubrene is chosen as a model system since its T-1 is far below S-1 and T-2 is resonant with S-1. This hot exciton process opens an additional route, marked as Dexter energy transfer channel ((CT)-C-3 -> T-2 -> S-1, DET channel), together with the well-known Forster resonance energy transfer channel ((CT)-C-1 -> S-1) to transfer the host energy to the guest. With proper approximates, the DET channel assisted by the hot excitons process can contribute about 46.6% excitons to rubrene S-1 and 83.4% rubrene emission in rubrene-doped devices. These studies set an in situ normative characterizing frame to visualize the hot excitons process in OLEDs. Published under an exclusive license by AIP Publishing.

• Institution
  华中科技大学